Guidewires and thin film catheter-sheaths and method of making same

ABSTRACT

Guidewires and thin-film catheter-sheaths, fabricated using vacuum deposition techniques, which are monolayer or plural-layer members having ultra-thin wall thicknesses to provide very-low profile delivery assemblies for introduction and delivery of endoluminal devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 09/443,929 which was filed on Nov. 19, 1999 now U.S. Pat. No.6,379,383, the disclosure of which is hereby incorporated by reference.This application also claims the benefit of U.S. Provisional PatentApplication No. 60/318,730 which was filed on Sep. 12, 2001.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of medical devices,and more particularly to guiding means such as a guidewire for advancinga catheter within a body lumen to perform a minimally invasive proceduresuch as percutaneous transluminal coronary angioplasty (PTCA). Thepresent invention further pertains to catheters and sheaths fordelivering and deploying an implantable device within a body lumen.

In a typical PTCA procedure a guiding catheter having a preformed distaltip is percutaneously introduced into the cardiovascular system of apatient by means of a conventional Seldinger technique and advancedproximally until the distal tip of the guiding catheter is seated in theostium of a desired coronary artery. A guidewire is positioned within aninner lumen of a dilatation catheter and then both are advanced throughthe guiding catheter to the distal end thereof. The guidewire is firstadvanced out of the distal end of the guiding catheter into thepatient's coronary vasculature until the distal end of the guidewirecrosses a lesion to be dilated, then the dilatation catheter having aninflatable balloon on the distal portion thereof is advanced into thepatient's coronary anatomy over the previously introduced guidewireuntil the balloon of the dilatation catheter is properly positionedacross the lesion. Once in position across the lesion, the balloon isinflated one or more times to a predetermined size with radiopaque fluidto compress the arteriosclerotic plaque of the lesion against the insideof the artery wall and to otherwise expand the inner lumen of theartery. The balloon is then deflated so that blood flow resumes throughthe dilated artery and the dilatation catheter is removed.

In a conventional stent delivery procedure, a stent is deliveredendoluminally on a delivery catheter, then expanded either by anangioplasty balloon or by removing a constraining sheath and permittingthe stent to radially expand by its shape memory, superelastic orself-expanding properties. Conventional guidewires for angioplasty andstent-delivery procedures usually comprise an elongated core member withthe distal portion of the core member having one or more taperedsections and a flexible body such as a helical coil disposed about thedistal portion of the core member. A shapeable member, which may be thedistal extremity of the core member or a separate shaping ribbon whichis secured to the distal extremity of the core member extends throughthe flexible body and is secured to a rounded plug at the distal end ofthe flexible body. Torquing means are provided on the proximal end ofthe core member to rotate, and thereby steer, the guidewire while it isbeing advanced through a patient's vascular system.

Further details of guidewires can be found in U.S. Pat. No. 4,516,972(Samson); U.S. Pat. No. 4,538,622 (Samson, et al.); U.S. Pat. No.4,554,929 (Samson, et al.); U.S. Pat. No. 4,616,652 (Simpson); U.S. Pat.No. 4,748,986 (Morrison et al.); U.S. Pat. No. 5,135,503 (Abrams); U.S.Pat. No. 5,341,818 (Abrams et al.); and U.S. Pat. No. 5,411,476 (Abramset al.) each of which is hereby incorporated herein in their entirety byreference thereto.

A major requirement for guidewires and other intraluminal guidingmembers, whether they be solid wire or tubular members, is that theyhave sufficient column strength to be pushed through a patient'svascular system or other body lumen without kinking. However, they mustalso be flexible enough to pass through tortuous passageways withoutdamaging the blood vessel or other body lumen through which they areadvanced. Efforts have been made to improve both the strength andflexibility of guidewires in order to make them more suitable for theirintended uses, but these two properties tend to be diametrically opposedto one another in that an increase in one usually involves a decrease inthe other.

The prior art makes reference to the use of alloys such as NITINOL(nickel-titanium alloy) which have shape memory and/or superelastic orpseudoelastic characteristics in medical devices which are designed tobe inserted into a patient's body. The shape memory characteristicsallow the prior art devices to be deformed while in the martensite phaseto facilitate their insertion into a body lumen or cavity and then beheated within the body to transform the metal to the austenite phase sothat the device returns to its remembered shape or to exert a force onwhatever prevents the device from returning to its zero strainconfiguration. Superelastic characteristics on the other hand generallyallow the metal to be deformed and restrained in the deformed conditionto facilitate the insertion of the medical device containing the metalinto a patient's body, with such deformation causing the phasetransformation, e.g. austenite to martensite. Once within the body lumenthe restraint on the superelastic member can be removed, therebyreducing the stress therein so that the superelastic member can returnto its original undeformed shape by the transformation back to theoriginal austenite phase or so that the superelastic member can exert aforce on whatever prevents the superelastic member from returning to itszero strain configuration. In other applications, the stress inducedaustenite to martensite transformation is utilized to minimize traumawhile advancing a medical device such as a guidewire within a patient'sbody lumen.

Shape memory or superelastic alloys generally have at least two phases,a martensite phase, which has a relatively low strength and which isstable at relatively low temperatures and higher strains, and anaustenite phase, which has a relatively high strength and which isstable at temperatures higher and strains lower than the martensitephase. Shape memory characteristics are imparted to the alloy by heatingthe metal at a temperature above body temperature, preferably betweenabout 40° to about 60° C., while the metal is kept in a constrainedshape and then cooled to ambient temperature. The cooling of the alloyto ambient temperature causes at least part of the austenite phase totransform to the martensite phase which is more stable at thistemperature. The constrained shape of the metal during this heattreatment is the shape programmed when the alloy is reheated to thesetemperatures causing the transformation of the martensite phase to theaustenite phase. The metal in the martensite phase may be plasticallydeformed to facilitate the entry thereof into a patient's body. Themetal will remain in the pre-programmed shape even when cooled to atemperature below the transformation temperature back to the martensitephase, so it must be reformed into a more usable shape, if necessary.Subsequent heating of the deformed martensite phase to a temperatureabove the martensite to austenite transformation temperature causes thedeformed martensite phase to transform to the austenite phase and duringthis phase transformation the metal reverts back to its remembered shapeor to exert a force on whatever prevents the device from returning toits zero strain configuration.

When stress is applied to a specimen of a metal such as NITINOL®exhibiting superelastic characteristics at a temperature at or abovewhich the transformation of martensite phase to the austenite phase iscomplete, the specimen deforms elastically until it reaches a particularstress level where the alloy then undergoes a stress-induced phasetransformation from the austenite phase to the martensite phase. As thephase transformation proceeds, the alloy undergoes significant increasesin strain but with little or no corresponding increases in stress. Thestrain increases while the stress remains essentially constant until thetransformation of the austenite phase to the martensite phase iscomplete. Thereafter, further increase in stress is necessary to causefurther deformation. The martensitic metal first yields elastically uponthe application of additional stress and then plastically with permanentresidual deformation.

If the load on the specimen is removed before any permanent deformationhas occurred, the martensitic specimen will elastically recover andtransform back to the austenite phase. The reduction in stress firstcauses a decrease in strain. As stress reduction reaches the level atwhich the martensite phase transforms back into the austenite phase, thestress level in the specimen will remain essentially constant (butsubstantially less than the constant stress level at which the austenitetransforms to the martensite) until the transformation back to theaustenite phase is complete, i.e., there is significant recovery instrain with only negligible corresponding stress reduction. After thetransformation back to austenite is complete, further stress reductionresults in elastic strain reduction. This ability to incur significantstrain at relatively constant stress upon the application of a load andto recover from the deformation upon the removal of the load is commonlyreferred to as superelasticity or pseudoelasticity.

The prior art makes reference to the use of metal alloys havingsuperelastic characteristics in medical devices which are intended to beinserted or otherwise used within a patient's body. See for example,U.S. Pat. No. 4,665,906 (Jervis) and U.S. Pat. No. 4,925,445 (Sakamotoet al). The Sakamoto et al. patent discloses the use of anickel-titanium superelastic alloy in an intravascular guidewire whichcould be processed to develop relatively high yield strength levels.However, at the relatively high yield stress levels which cause theaustenite-to-martensite phase transformation characteristic of thematerial, it did not have a very extensive stress-induced strain rangein which the austenite transforms to martensite at relative constantstress. As a result, frequently as the guidewire was being advancedthrough a patient's tortuous vascular system, it would be stressedbeyond the superelastic region, i.e. develop a permanent set or evenkink which can result in tissue damage. This permanent deformation wouldgenerally require the removal of the guidewire and the replacementthereof with another. Products of the Jervis patent on the other handhad extensive strain ranges, i.e. 2 to 8% strain, but the relativelyconstant stress level at which the austenite transformed to martensitewas very low, e.g. 50 ksi.

The prior methods of using the shape memory characteristics of thesealloys in medical devices intended to be placed within a patient's bodypresented operational difficulties. For example, with shape memoryalloys having a stable martensite temperature below body temperature, itwas frequently difficult to maintain the temperature of the medicaldevice containing such an alloy sufficiently below body temperature toprevent the transformation of the martensite phase to the austenitephase when the device was being inserted into a patient's body. Withintravascular devices formed of shape memory alloys havingmartensite-to-austenite transformation temperatures well above bodytemperature, the devices could be introduced into a patient's body withlittle or no problem, but they had to be heated to themartensite-to-austenite transformation temperature which was frequentlyhigh enough to cause tissue damage and very high levels of pain.

What has been needed and heretofore unavailable is tubular body forintravascular devices, such as guidewires or catheter-sheaths, whichhave at least a portion thereof exhibiting superelastic and/or shapememory characteristics and which is fabricated by vacuum depositiontechniques to provide precise control over the crystalline structure ofthe material used to fabricate the device.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a method of manufacturing a guidewireor a catheter-sheath, each having a body. The body of the inventiveguidewire can be generally tubular and define a central lumen or,alternatively, can be solid. The body of the inventive catheter-sheathis generally tubular and defines a central lumen. The method ofmanufacturing the inventive guidewire or catheter-sheath comprisesproviding a substrate having a surface capable of accommodating metaldeposition thereon and having a substrate geometry corresponding atleast in part to a geometry desired for the body, depositing a thin-filmof a biocompatible metal onto the substrate using a vacuum depositiontechnique, the thin-film forming the body, and removing the substratefrom the body. The method optionally further comprises subjecting thebody to post-deposition annealing.

The vacuum deposition technique can be any vacuum deposition techniquesuch as ion beam-assisted evaporative deposition or sputter deposition(e.g., cylindrical magnetron sputter deposition). In a preferredembodiment, ion beam-assisted evaporative deposition is used and isconducted in the presence of an inert gas such as, for example, argon,xenon, nitrogen, and neon.

In one embodiment, a sacrificial layer is deposited onto the substrateprior to the deposition of the biocompatible metal. Alternatively, thesubstrate itself comprises a sacrificial material. Removal of thesubstrate is accomplished by any suitable method, such as etching thesacrificial material. In certain embodiments, the substrate geometry isgenerally cylindrical having a circular transverse cross-section or,alternatively, an elliptical transverse cross-section.

The biocompatible metal can be selected from the group consisting ofelemental titanium, vanadium, aluminum, nickel, tantalum, zirconium,chromium, silver, gold, silicon, magnesium, niobium, scandium, platinum,cobalt, palladium, manganese, molybdenum and alloys thereof, nitinol,and stainless steel.

In one embodiment, the deposition process is repeated a plurality oftimes to form a plurality of successive layers of the deposited metal.In a preferred embodiment, the successive layers are concentric. Inanother embodiment, a radiopaque metal is used to form at least one ofthe layers.

The invention also relates to a guidewire having a body comprising athin-film of a biocompatible metal formed by a vacuum depositiontechnique. In certain embodiments of the inventive guidewire, thethin-film comprises a plurality of layers. The invention further relatesto a catheter-sheath having a generally tubular body, the bodycomprising a thin-film of a biocompatible metal formed by a vacuumdeposition technique. In certain embodiments of the inventivecatheter-sheath, the thin-film comprises a plurality of layers.

The invention also relates to an assembly for delivering a medicaldevice via a patient's vascular system. The inventive assembly comprises(a) a medical device, (b) a guidewire having a guidewire body, theguidewire body comprising a first thin-film of a first biocompatiblemetal formed by a vacuum deposition technique, and (c) a catheter-sheathhaving generally tubular catheter-sheath body, the catheter-sheath bodycomprising a second thin-film of a second biocompatible metal formed bya vacuum deposition technique, the catheter-sheath body defining acatheter-sheath lumen. The assembly is formed by positioning theguidewire coaxially within the lumen of the catheter-sheath andconcentrically positioning the medical device within the lumen of thecatheter-sheath and intermediate between the catheter-sheath body andthe guidewire body. The first and second biocompatible metals can be thesame metal or different metals. In one embodiment at least one of thefirst thin-film and the second thin-film comprises a plurality oflayers. In an alternative embodiment, the first thin-film and the secondthin-film each comprise a plurality of layers. In a preferredembodiment, a radiopaque metal is used to form at least one of thelayers. The medical device can be any medical device that can bedelivered via a patient's vascular system, for example, a stent, agraft, a stent-graft, a valve, a filter, an occluder, and a patch.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the invention, will be better understood whenread in conjunction with the appended drawings. For the purpose ofillustrating the invention, there is shown in the drawings embodimentswhich are presently preferred. It should be understood, however, thatthe invention is not limited to the precise arrangements andinstrumentalities shown.

FIG. 1 is a side-elevational cross-sectional view of a guidewire inaccordance with the present invention.

FIG. 2 is a side-elevational cross-sectional view of a second embodimentof a guidewire in accordance with the present invention.

FIG. 3 is a side-elevational cross-sectional view of a thin-filmcatheter-sheath in accordance with the present invention.

FIG. 4 is a side-elevational cross-sectional view of a thin-filmcatheter-sheath positioned concentrically about an inventive guidewire.

FIGS. 5A–5C illustrate a further embodiment of the thin-filmcatheter-sheath and/or guidewire incorporating microperforations ofvarious patterns in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to guidewires and to thin-filmcatheter-sheaths, wherein each of the guidewire and the thin-filmcatheter-sheath is fabricated by vacuum deposition techniques, similarto those employed in the microelectronics arts to fabricatesemiconductors. Each of the guidewire and the catheter-sheath has a bodywhich is preferably formed either as a single layer tubular member or asa laminated tubular member with plural layers, wherein the layers can beconcentrically aligned.

The inventive guidewires and catheter-sheaths provide several advantagesover the prior art. Specific examples of such advantages of theinventive metal catheter-sheaths and thin-film guidewires, include: (i)metal catheter-sheaths have the same metallic creep rate as theself-expanding devices that they constrain so they are less likely todeform and take a set during sterilization or during the shelf-life ofthe product; (ii) by controlling material properties and employingmicro-perforations it is possible to impart radial, longitudinal ormulti-directional compliance to the catheter-sheath or guidewire suchthat compliance and or flexibility is constant or varied over the lengthof the device; (iii) when vacuum deposition is employed in preference toconventional wrought processes and materials, the chemical content,microstructure, mechanical properties, etc., can be precisely controlledthroughout the thickness of the film and along the entire length of thedevice, as opposed to the prior art which requires fusion of multiplesections to impart certain mechanical properties, microstructure, orchemical content; (iv) in addition to providing single layer thin-filmdevices, the present invention provides for fabricating multi-layerdevices which exhibit improved strength, biocompatibility, corrosionresistance, fatigue resistance, radiopacity, trackability, pushabilityand interactions with other medical devices or anatomical structures;and (v) vacuum deposition processes lend themselves to fabricatingthinner devices and devices with improved wall thickness uniformity.

The mechanical properties of metals depend significantly on theirmicrostructure. The forming and shaping processes used to fabricatemetal foils, wires and thin-walled seamless tubes involves heavydeformation of a bulk material, which results in a heavily strained anddeformed grain structure. Even though annealing treatments may partiallyalleviate the grain deformation, it is typically impossible to revert towell-rounded grain structure and a large range of grain sizes is acommon result. The end result of conventional forming and shapingprocesses, coupled with annealing, typically results in non-uniformgrain structure and less favorable mechanical properties in smallersized wrought metal products. It is possible, therefore, to produce highquality small sized metal products with a homogeneous crystallinestructure for a variety of purposes, such as micromechanical devices andmedical devices, using vacuum deposition technologies.

In vacuum deposition technologies, materials are formed directly in thedesired geometry, e.g., planar, tubular, etc. The common principle ofthe vacuum deposition processes is to take a material in a minimallyprocessed form (a source material), such as pellets or thick foils, andatomize the material. Atomization may be carried out using heat, as isthe case in physical vapor deposition, or using the effect ofcollisional processes, as in the case of sputter deposition, forexample. In some forms of deposition, a process such as laser ablation,which creates microparticles which typically comprise one or more atoms,may replace atomization. Using laser ablation, the number of atoms perparticle may be in the thousands or more. The atoms or microparticles ofthe source material are then deposited on a substrate or mandrel todirectly form the desired object. In other deposition methodologies,chemical reactions between ambient gas introduced into the vacuumchamber, i.e., the gas source, and the deposited atoms and/or particlesare part of the deposition process. In this scenario, the depositedmaterial includes compound species that are formed due to the reactionof the solid source and the gas source, such as in the case of chemicalvapor deposition. In most cases, the deposited material is then eitherpartially or completely removed from the substrate thereby releasing thedesired product.

The rate of film growth is a significant parameter of vacuum depositionprocesses. In order to deposit materials that can be compared infunctionality with wrought metal products, deposition rates in excess of1 micrometers/hour are a must and indeed rates as high as 100micrometers per hour are desirable. These are high deposition rates andit is known that at such rates the deposits always have a columnarstructure. Depending on other deposition parameters, and mostimportantly on the substrate temperature, the columns may be amorphousor crystalline, but at such high deposition rates microcrystallinestructure development can be expected at best. The difficulty is thatthe columns provide a mechanically weak structure in which crackpropagation can occur uninhibited across the whole thickness of thedeposit.

A special advantage of vacuum deposition technologies is that it ispossible to deposit layered materials and thus films possessingexceptional qualities may be produced (c.f., H. Holleck, V. Schier:“Multilayer PVD coatings for wear protection”, Surface and CoatingsTechnology, Vol. 76–77 (1995) pp. 328–336). Layered materials, such assuperstructures or multilayers, are commonly deposited to take advantageof some chemical, electronic, or optical property of the material as acoating; a common example is an antireflective coating on an opticallens.

It has not been recognized until relatively recently that multilayercoatings may have improved mechanical properties compared with similarcoatings made of a single layer. The improved mechanical properties maybe due to the ability of the interface between the layers to relievestress. This stress relief occurs if the interface provides a slideplane, is plastic, or may delaminate locally. This property ofmultilayer films has been recognized in regard with their hardness butthis recognition has not been translated to other mechanical propertiesthat are significant for metal products that may be used in applicationwhere they replace conventional wrought metal parts.

The process according to the invention can be modified by interruptingfilm growth at various layers thereby resulting in discontinuous columnsthat prevent crack propagation across the entire film thickness. In thissense, it is not necessary that the structure comprise a multiplicity ofchemically distinct layers, as is common in the case of thin filmtechnology where multilayers are used. Such chemical differences may beuseful and may contribute to improved properties of the materials.

In its simplest form, the process of fabricating the inventivemultilayer devices comprises the steps of providing a substrate,depositing a first layer of material on the substrate, depositing asecond layer of material on the first layer of material and optionallyremoving the layered material from the substrate. In more complex cases,the number of layers is more than two. There is no limitation regardingthe number of layers and regarding the thickness of each layer.

As used in this application a “layer” is intended to mean asubstantially uniform material limited by interfaces between it andadjacent other substantially homogeneous layers, substrate, orenvironment. The interface region between adjacent layers is aninhomogeneous region in which extensive thermodynamic parameters maychange. Different layers are not necessarily characterized by differentvalues of the extensive thermodynamic parameters but at the interface,there is a local change at least in some parameters. For example, theinterface between two steel layers that are identical in composition andmicrostructure may be characterized by a high local concentration ofgrain boundaries due to an interruption of the film growth process.Thus, the interface between layers is not necessarily different inchemical composition if it is different in structure.

It is necessary to provide for good adhesion between the layers and thisis usually achieved by providing for a relatively broad interface regionrather than for an abrupt interface region. The width of the interfaceregion may be defined as the range within which extensive thermodynamicparameters change. This range can depend on the interface areaconsidered and it may mean the extent of interface microroughness. Inother words, adhesion may be promoted by increased interfacemicroroughness between adjacent layers.

By providing for a layered structure, the inventive materials comprise acontrolled maximum size of grains and columns as extended defects in thedirection of the film growth (perpendicular to the layers). This limitof the grain or defect size results in materials that have increasedmechanical strength and particularly increased toughness compared totheir non-laminated counterparts, both deposited and wrought materials.In addition, by limiting the extent to which defects and grainboundaries reach across the laminate, corrosion resistance is alsoimproved.

Laminated materials will have additional advantages when chemicalcompositions of the layers are chosen to achieve special properties. Forexample, a radiopaque material such as Ta may form one layer of astructure while other layers are chosen to provide the material withnecessary mechanical and other properties.

In accordance with a preferred embodiment the present invention, thepreferred deposition methodologies include ion-beam assisted evaporativedeposition and sputter deposition techniques. In ion beam-assistedevaporative deposition it is preferable to employ dual and simultaneousthermal electron beam evaporation with simultaneous ion bombardment ofthe material being deposited using an inert gas, such as argon, xenon,nitrogen or neon. Bombardment with inert gas ions during depositionserves to reduce void content by increasing the atomic packing densityin the deposited material. The reduced void content in the depositedmaterial allows the mechanical properties of that deposited material tobe similar to bulk material properties. Deposition rates up to 20nanometers per second (nm/sec) are achievable using ion beam-assistedevaporative deposition techniques.

Materials to make the inventive guidewires and thin-filmcatheter-sheaths are chosen for their biocompatibility, mechanicalproperties, i.e., tensile strength, yield strength, and their ease ofdeposition. Examples of such materials include, but are not limited to,elemental titanium, vanadium, aluminum, nickel, tantalum, zirconium,chromium, silver, gold, silicon, magnesium, niobium, scandium, platinum,cobalt, palladium, manganese, molybdenum and alloys thereof, such aszirconium-titanium-tantalum alloys, nitinol, and stainless steel.

The guidewires and thin-film catheter-sheaths of the invention arepreferably fabricated of nickel-titanium alloys, and may be doped orlaminated with radiopaque materials, such as tantalum (Ta) to enhancethe radiopacity of the guidewire under fluoroscopy. In one embodiment,the inventive guidewires and thin-film catheter-sheaths preferably haveshape memory or superelastic properties. By way of example, a method offorming the elongated shape memory or superelastic portion of theguidewire or thin-film catheter-sheath can include fabricating agenerally tubular member by vacuum depositing nickel-titanium alloy ontoa suitable cylindrical substrate, removing the deposited tubular memberfrom the substrate, then heat treating the deposited material at a giventemperature between about 450° to about 600° C., preferably about 475°to about 550° C., for between about 0.5 to about 60 minutes to generatesuperelastic properties. To impart a shape memory, either the entirematerial or a region or regions of the deposited material can besubjected to shaping stress equal to between about 5% to about 50%,preferably about 10% to about 30%, of the yield stress of the material(as measured at room temperature) during a heat treatment of about 450°to about 600° C. This thermomechanical processing pre-programs a shapememory for the pre-programmed shape to the material and providesrelatively uniform residual stress in the material. It is preferablethat the alloy composition and thermal treatment are selected to providean austenite finish transformation temperature generally about −20° C.to about 40° C. and usually less than body temperature (approximately37° C.). To obtain more consistent final properties, the material may beannealed after deposition. Although an exemplary method of forming theelongated shape memory or superelastic portion of the guidewire orthin-film catheter-sheath has been given, it is to be understood thatthe present invention is not limited to this particular method, or thegiven values.

In accordance with a method of the present invention, vacuum depositionmethods as are known in the microelectronics and nano-fabrication artsare preferably employed. It is preferable to employ sputtering or ionbeam-assisted evaporative deposition to deposit at least one metal filmof a biocompatible metal onto a sacrificial substrate. The substrate hasa geometry corresponding to the geometry desired for the guidewireand/or thin-film catheter-sheath, e.g., to create tubular body having acircular or elliptical transverse cross-sectional shape, at least onelayer of a thin-film of a biocompatible metal is deposited onto thesacrificial substrate. When multiple layers are to be deposited, eachlayer may have varying properties along the length of the device byvarying the local deposition conditions. For example, locally doping thetarget material with Ti in the case of nitinol deposition to raise thetransition temperature, with Ta to increase radiopacity, or with aradioactive isotope to cause local radioactivity. After depositing atleast one layer having a desired thickness, the substrate and thedeposited thin-film of metal are removed from the deposition chamber andthe sacrificial substrate is removed by means suitable for the selectedsubstrate. For example, if a copper substrate is employed, it can beremoved by chemical etching. Alternatively, a sacrificial layer of amaterial, such as carbon or aluminum, may be deposited on the externalsurface of the substrate prior to depositing the metal. After depositionhas occurred, the sacrificial layer can be removed by any suitableprocess or means, such as, for example, melting, chemical means,ablation, or machining, to free the guidewire or catheter-sheath fromthe substrate. The entire guidewire or a selected region (or selectedregions) of the guidewire may be subject to post-deposition annealing toalter the crystalline structure of the thin-film and effect changes inthe material properties of the metal film, such as altering thetransition temperature of the annealed regions.

Turning now to the accompanying figures, FIGS. 1 and 2 depict twoembodiments of the inventive guidewire 10. In FIG. 1 there is depicted aguidewire body 12 comprising a monolayer of material formed by a vacuumdeposition technique, although conventional wrought processes may beemployed for certain embodiments such as those where compliance isrequired. The generally tubular guidewire body 12 has a centralguidewire lumen 14 and an outer diameter d₁.

FIG. 2 depicts a guidewire 10 having a guidewire body 12 comprising aplurality of layers 12 a and 12 b formed by a vacuum depositiontechnique. The guidewire body 12 defines a central guidewire lumen 14.Those skilled in the art will understand that an inventive guidewire 10having plural layers may be fabricated with at least two layers (12 aand 12 b) or any number of layers more than two. Additionally, each ofthe layers may be either continuous or discontinuous about thecircumference or length of the tubular guidewire body 12. Variations incontinuity or discontinuity of an individual layer can be imparted inorder to impart differential material and performance properties to theguidewire 10. A guidewire 10 according to the present inventionpreferably has an outer diameter d₁ between about 0.2 millimeters (mm)to about 0.75 millimeters (mm), with a wall thickness between about 0.1micrometer to about 75 micrometers.

FIG. 3 illustrates an embodiment of the inventive thin-filmcatheter-sheath 20 comprising a tubular catheter-sheath body 22 defininga central catheter-sheath lumen 24. Like the guidewire 10, the thin-filmcatheter-sheath 20 is fabricated by vacuum deposition of a biocompatiblemetal, preferably a nickel-titanium alloy, although conventional wroughtprocess may be employed for certain embodiments such as those wherecompliance is required. The tubular catheter-sheath body 22 can be amonolayer of deposited material, or can comprise a plurality oflaminated layers (not shown). A thin-film catheter-sheath according tothe present invention preferably has an inner diameter d₂ between about0.25 millimeters (mm) to about 6 millimeters (mm) to accommodate a widerange of self-expanding stents or other implantable and non-implantablemedical devices such as filters, occlusion devices, valves, snarebaskets, etc. Like the inventive guidewires, a thin-film catheter-sheathaccording to the present invention preferably has a wall thicknessbetween about 0.1 micrometers to 75 micrometers.

Referring now to FIG. 4, there is depicted a medical device deliveryassembly 30 comprising a guidewire body 12 defining central guidewirelumen 14, a thin-film catheter-sheath body 22 defining centralcatheter-sheath lumen 24 concentrically positioned coaxially about theguidewire body 12 and a stent 32 which is concentrically positionedwithin central catheter-sheath lumen 24 and intermediate between thethin-film catheter-sheath body 22 and the guidewire body 12 andconstrained therein by the thin-film catheter-sheath 20. The medicaldevice used with the delivery assembly can be any medical device thatcan be delivered via a patient's vascular system, for example, a stent(as shown in FIG. 4), a graft, a stent-graft, a valve, a filter, anoccluder, and a patch.

Turning now to FIGS. 5A–5C, a guidewire and/or catheter-sheath inaccordance with a further embodiment of the invention is illustrated. Asshown in FIG. 5A, an embodiment of the inventive guidewire orcatheter-sheath is depicted in which areas of a guidewire orcatheter-sheath body has microperforations. Microperforations, such asthose referred to as 100 in FIGS. 5A and 5B impart longitudinalcompliance, whereas microperforations such as those referred to as 110in FIGS. 5A and 5C impart radial compliance. With particular referenceto FIG. 5B, microperforations in the form of diamond shaped slots 100around the circumference of the guidewire or catheter-sheath areprovided to increase the longitudinal compliance of the guidewire orcatheter-sheath in tension and compression thereby providing flexibilityto negotiate tight radii. FIG. 5C shows how microperforations in theform of longitudinal slots 110 provide for radial compliance. In orderto achieve desired compliance characteristics along the length of thecatheter-sheath or guidewire, the microperforation (slot) patterns canbe used in conjunction with one another in alternating patterns and/orleaving unpatterned sections along the length of the guidewire. Thoseskilled in the art will recognize that there are a number of differentgeometric patterns that can be used to form the microperforations, otherthan those described here, that will provide desired compliancecharacteristics to the inventive guidewire or catheter-sheath discussedherein. Skilled artisans will also recognize that microperforations canbe created by any suitable technique such as etching a metal film, orduring a vacuum deposition process by either masking a substrate duringdeposition, or etching a substrate to provide the pattern which willform the microperforations once the deposition has occurred.

In accordance with a preferred embodiment the present invention, thepreferred vacuum deposition technique is selected from the groupconsisting of ion-beam assisted evaporative deposition and sputteringtechniques. In ion beam-assisted evaporative deposition it is preferableto employ dual and simultaneous thermal electron beam evaporation withsimultaneous ion bombardment of the material being deposited using aninert gas, such as argon, xenon, nitrogen or neon. Bombardment withinert gas ions during deposition serves to reduce void content byincreasing the atomic packing density in the deposited material. Thereduced void content in the deposited material allows the mechanicalproperties of that deposited material to be similar to the bulk materialproperties. Deposition rates up to 20 nanometers per second (nm/sec) areachievable using ion beam-assisted evaporative deposition techniques.

As used in this application, the articles “a” and “an” refer to one ormore than one (i.e., to at least one) of the grammatical objects of thearticle. By way of example, “an element” means one element or more thanone element.

EXAMPLE 1

In accordance with the preferred embodiment of fabricating the inventivemicroporous metallic implantable device in which the device isfabricated from vacuum deposited nitinol tube, a cylindricaldeoxygenated copper substrate is provided. The substrate is mechanicallyand/or electropolished to provide a substantially uniform surfacetopography for accommodating metal deposition thereupon. A cylindricalhollow cathode magnetron sputtering deposition device was employed, inwhich the cathode was on the outside and the substrate was positionedalong the longitudinal axis of the cathode. A cylindrical targetconsisting either of a nickel-titanium alloy having an atomic ratio ofnickel to titanium of about 50—50% and which can be adjusted by spotwelding nickel or titanium wires to the target, or a nickel cylinderhaving a plurality of titanium strips spot welded to the inner surfaceof the nickel cylinder, or a titanium cylinder having a plurality ofnickel strips spot welded to the inner surface of the titanium cylinderis provided. It is known in the sputter deposition arts to cool a targetwithin the deposition chamber by maintaining a thermal contact betweenthe target and a cooling jacket within the cathode. In accordance withthe present invention, it has been found useful to reduce the thermalcooling by thermally insulating the target from the cooling jacketwithin the cathode while still providing electrical contact to it. Byinsulating the target from the cooling jacket, the target is allowed tobecome hot within the reaction chamber. Two methods of thermallyisolating the cylindrical target from the cooling jacket of the cathodewere employed. First, a plurality of wires having a diameter of 0.0381mm were spot welded around the outer circumference of the target toprovide an equivalent spacing between the target and the cathode coolingjacket. Second, a tubular ceramic insulating sleeve was interposedbetween the outer circumference of the target and the cathode coolingjacket. Further, because the Ni—Ti sputtering yields can be dependant ontarget temperature, methods which allow the target to become uniformlyhot are preferred.

The deposition chamber was evacuated to a pressure less than or about2.5×10⁻⁷ Torr and pre-cleaning of the substrate is conducted undervacuum. During the deposition, substrate temperature is preferablymaintained within the range of 300 and 700 degrees Centigrade. It ispreferable to apply a negative bias voltage between 0 and −1000 volts tothe substrate, and preferably between −50 and −150 volts, which issufficient to cause energetic species arriving at the surface of thesubstrate. During deposition, the gas pressure is maintained between 0.1and 40 mTorr but preferably between 1 and 20 mTorr. Sputteringpreferably occurs in the presence of an Argon atmosphere. The argon gasmust be of high purity and special pumps may be employed to reduceoxygen partial pressure. Deposition times will vary depending upon thedesired thickness of the deposited tubular film. After deposition, theplurality of microperforations are formed in the tube by removingregions of the deposited film by etching, such as chemical etching,ablation, such as by excimer laser or by electric discharge machining(EDM), or the like. After the plurality of microperforations are formed,the formed microporous film is removed from the copper substrate byexposing the substrate and film to a nitric acid bath for a period oftime sufficient to remove or dissolve the copper substrate.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. An assembly for delivering a medical device via a patient's vascularsystem, the assembly comprising: (a) a medical device; (b) a guidewirehaving a guidewire body, the guidewire body comprising a first thin-filmof a first biocompatible metal formed by a vacuum deposition technique;and (c) a catheter-sheath having generally tubular catheter-sheath body,the catheter-sheath body comprising a second thin-film of a secondbiocompatible metal formed by a vacuum deposition technique, thecatheter-sheath body defining a catheter-sheath lumen; wherein theguidewire is positioned coaxially within the lumen of thecatheter-sheath, and wherein the medical device is concentricallypositioned within a distal portion of the catheter-sheath lumen andintermediate the catheter-sheath body and the guidewire body, therebyforming the assembly, wherein at least one of the first thin-film andthe second thin-film comprises a plurality of layers.
 2. The assembly ofclaim 1, wherein the guidewire body is generally tubular.
 3. Theassembly of claim 1, wherein at least one of the guidewire body and thecatheter-sheath body further comprises a plurality of microperforationsthat impart at least one of longitudinal compliance and radialcompliance.
 4. The assembly of claim 1, wherein the first and secondbiocompatible metals are similar.
 5. The assembly of claim 1, whereinthe medical device is selected from the group consisting of a stent, agraft, a stent-graft, a valve, a filter, an occluder, and a patch. 6.The assembly of claim 1, wherein a radiopaque metal is used to form atleast on the layers.
 7. The assembly of claim 1, wherein the first-thinfilm and the second thin-film each comprise a plurality of layers.
 8. Anassembly for delivering a medical device via a patient's vascularsystem, the assembly comprising: (a) a medical device; (b) a guidewirehaving a guidewire body, the guidewire body comprising a first thin-filmof a first biocompatible metal formed by a vacuum deposition technique;and (c) a catheter-sheath having generally tubular catheter-sheath body,the catheter-sheath body comprising a second thin-film of a secondbiocompatible metal formed by a vacuum deposition technique, thecatheter-sheath body defining a catheter-sheath lumen; wherein theguidewire is positioned coaxially within the lumen of thecatheter-sheath, and wherein the medical device is concentricallypositioned within a distal portion of the catheter-sheath lumen andintermediate the catheter-sheath body and the guidewire body, therebyforming the assembly, wherein the first thin-film and the secondthin-film each comprise a plurality of layers.
 9. The assembly of claim8, wherein the guidewire body is generally tubular.
 10. The assembly ofclaim 8, wherein at least one of the guidewire body and thecatheter-sheath body further comprises a plurality of microperforationsthat impart at least one of longitudinal compliance and radialcompliance.
 11. The assembly of claim 8, wherein the first and secondbiocompatible metals are similar.
 12. The assembly of claim 8, whereinthe medical device is selected from the group consisting of a stein, agraft, a stent-graft, a valve, a filter, an occiuder, and a patch. 13.The assembly of claim 8, wherein a radiopaque metal is used to form atleast on the layers.